"Your cells, your macro molecules, are literally made up of protein, fat, carbohydrates, nucleic acids,'' she said. "When you do not eat one of the three macro nutrients — those three things I just mentioned — you’re starving yourselves."

Al responded with some harsh words for the former "Biggest Loser" trainer on Twitter Thursday.

So @JillianMichaels says #Keto is a bad idea. This from a woman who promoted on camera bullying , deprivation, manipulation and more weekly in the name of weight loss. Now those sound like bad ideas

He said on Friday that Michaels responded to his tweet with an email, but he didn't want to divulge her message because it was private. He did note that his health has been great since embarking on the diet.

"I've been checking blood work and vitals every month, and my cholesterol has gotten better,'' he said. "It was good to begin with. My blood pressure is great."

Al has embraced the keto lifestyle, including sharing his recipe for keto-approved muffins with Savannah Guthrie after the TODAY anchor turned him on to the diet.

Savannah spoke about her experience with Dr. Mehmet Oz on his show in November, saying she had less energy to work out due to the reduced carbohydrates but that her brain felt sharper throughout the day.

"In some ways you have to deprive yourself,'' Savannah said. "No carbs whatsoever, and that's really restrictive, but it's opened up some things that I would never let myself eat a lot of, such as cheese and bacon, so I like that."